/* Copyright 1998, 2011, 2013 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "ares_setup.h"

#ifdef HAVE_NETINET_IN_H
#  include <netinet/in.h>
#endif
#ifdef HAVE_NETDB_H
#  include <netdb.h>
#endif
#ifdef HAVE_ARPA_INET_H
#  include <arpa/inet.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#  include <arpa/nameser.h>
#else
#  include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#  include <arpa/nameser_compat.h>
#endif

#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif

#include "ares.h"
#include "ares_inet_net_pton.h"
#include "bitncmp.h"
#include "ares_platform.h"
#include "ares_nowarn.h"
#include "ares_private.h"

#ifdef WATT32
#undef WIN32
#endif

struct host_query {
	/* Arguments passed to ares_gethostbyname() */
	ares_channel channel;
	char *name;
	ares_host_callback callback;
	void *arg;
	int sent_family; /* this family is what was is being used */
	int want_family; /* this family is what is asked for in the API */
	const char *remaining_lookups;
	int timeouts;
};

static void next_lookup(struct host_query *hquery, int status_code);
static void host_callback(void *arg, int status, int timeouts,
	unsigned char *abuf, int alen);
static void end_hquery(struct host_query *hquery, int status,
	struct hostent *host);
static int fake_hostent(const char *name, int family,
	ares_host_callback callback, void *arg);
static int file_lookup(const char *name, int family, struct hostent **host);
static void sort_addresses(struct hostent *host,
	const struct apattern *sortlist, int nsort);
static void sort6_addresses(struct hostent *host,
	const struct apattern *sortlist, int nsort);
static int get_address_index(const struct in_addr *addr,
	const struct apattern *sortlist, int nsort);
static int get6_address_index(const struct ares_in6_addr *addr,
	const struct apattern *sortlist, int nsort);

void ares_gethostbyname(ares_channel channel, const char *name, int family,
	ares_host_callback callback, void *arg)
{
	struct host_query *hquery;

	/* Right now we only know how to look up Internet addresses - and unspec
	   means try both basically. */
	switch (family) {
	case AF_INET:
	case AF_INET6:
	case AF_UNSPEC:
		break;
	default:
		callback(arg, ARES_ENOTIMP, 0, NULL);
		return;
	}

	if (fake_hostent(name, family, callback, arg))
		return;

	/* Allocate and fill in the host query structure. */
	hquery = ares_malloc(sizeof(struct host_query));
	if (!hquery)
	{
		callback(arg, ARES_ENOMEM, 0, NULL);
		return;
	}
	hquery->channel = channel;
	hquery->name = ares_strdup(name);
	hquery->want_family = family;
	hquery->sent_family = -1; /* nothing is sent yet */
	if (!hquery->name) {
		ares_free(hquery);
		callback(arg, ARES_ENOMEM, 0, NULL);
		return;
	}
	hquery->callback = callback;
	hquery->arg = arg;
	hquery->remaining_lookups = channel->lookups;
	hquery->timeouts = 0;

	/* Start performing lookups according to channel->lookups. */
	next_lookup(hquery, ARES_ECONNREFUSED /* initial error code */);
}

static void next_lookup(struct host_query *hquery, int status_code)
{
	const char *p;
	struct hostent *host;
	int status = status_code;

	for (p = hquery->remaining_lookups; *p; p++)
	{
		switch (*p)
		{
		case 'b':
			/* DNS lookup */
			hquery->remaining_lookups = p + 1;
			if ((hquery->want_family == AF_INET6) ||
				(hquery->want_family == AF_UNSPEC)) {
				/* if inet6 or unspec, start out with AAAA */
				hquery->sent_family = AF_INET6;
				ares_search(hquery->channel, hquery->name, C_IN, T_AAAA,
					host_callback, hquery);
			}
			else {
				hquery->sent_family = AF_INET;
				ares_search(hquery->channel, hquery->name, C_IN, T_A,
					host_callback, hquery);
			}
			return;

		case 'f':
			/* Host file lookup */
			status = file_lookup(hquery->name, hquery->want_family, &host);

			/* this status check below previously checked for !ARES_ENOTFOUND,
			   but we should not assume that this single error code is the one
			   that can occur, as that is in fact no longer the case */
			if (status == ARES_SUCCESS)
			{
				end_hquery(hquery, status, host);
				return;
			}
			status = status_code;   /* Use original status code */
			break;
		}
	}
	end_hquery(hquery, status, NULL);
}

static void host_callback(void *arg, int status, int timeouts,
	unsigned char *abuf, int alen)
{
	struct host_query *hquery = (struct host_query *) arg;
	ares_channel channel = hquery->channel;
	struct hostent *host = NULL;

	hquery->timeouts += timeouts;
	if (status == ARES_SUCCESS)
	{
		if (hquery->sent_family == AF_INET)
		{
			status = ares_parse_a_reply(abuf, alen, &host, NULL, NULL);
			if (host && channel->nsort)
				sort_addresses(host, channel->sortlist, channel->nsort);
		}
		else if (hquery->sent_family == AF_INET6)
		{
			status = ares_parse_aaaa_reply(abuf, alen, &host, NULL, NULL);
			if ((status == ARES_ENODATA || status == ARES_EBADRESP ||
				(status == ARES_SUCCESS && host && host->h_addr_list[0] == NULL)) &&
				hquery->want_family == AF_UNSPEC) {
				/* The query returned something but either there were no AAAA
				   records (e.g. just CNAME) or the response was malformed.  Try
				   looking up A instead. */
				if (host)
					ares_free_hostent(host);
				hquery->sent_family = AF_INET;
				ares_search(hquery->channel, hquery->name, C_IN, T_A,
					host_callback, hquery);
				return;
			}
			if (host && channel->nsort)
				sort6_addresses(host, channel->sortlist, channel->nsort);
		}
		end_hquery(hquery, status, host);
	}
	else if ((status == ARES_ENODATA || status == ARES_EBADRESP ||
		status == ARES_ETIMEOUT) && (hquery->sent_family == AF_INET6 &&
			hquery->want_family == AF_UNSPEC))
	{
		/* The AAAA query yielded no useful result.  Now look up an A instead. */
		hquery->sent_family = AF_INET;
		ares_search(hquery->channel, hquery->name, C_IN, T_A, host_callback,
			hquery);
	}
	else if (status == ARES_EDESTRUCTION)
		end_hquery(hquery, status, NULL);
	else
		next_lookup(hquery, status);
}

static void end_hquery(struct host_query *hquery, int status,
	struct hostent *host)
{
	hquery->callback(hquery->arg, status, hquery->timeouts, host);
	if (host)
		ares_free_hostent(host);
	ares_free(hquery->name);
	ares_free(hquery);
}

/* If the name looks like an IP address, fake up a host entry, end the
 * query immediately, and return true.  Otherwise return false.
 */
static int fake_hostent(const char *name, int family,
	ares_host_callback callback, void *arg)
{
	struct hostent hostent;
	char *aliases[1] = { NULL };
	char *addrs[2];
	int result = 0;
	struct in_addr in;
	struct ares_in6_addr in6;

	if (family == AF_INET || family == AF_INET6)
	{
		/* It only looks like an IP address if it's all numbers and dots. */
		int numdots = 0, valid = 1;
		const char *p;
		for (p = name; *p; p++)
		{
			if (!ISDIGIT(*p) && *p != '.') {
				valid = 0;
				break;
			}
			else if (*p == '.') {
				numdots++;
			}
		}

		/* if we don't have 3 dots, it is illegal
		 * (although inet_addr doesn't think so).
		 */
		if (numdots != 3 || !valid)
			result = 0;
		else
		{
			//result = ((in.s_addr = inet_addr(name)) == INADDR_NONE ? 0 : 1);
			ULONG s_net_addr;
			ares_inet_pton(AF_INET, name, &s_net_addr);
			result = ((in.s_addr = s_net_addr) == INADDR_NONE ? 0 : 1);
		}
		if (result)
			family = AF_INET;
	}
	if (family == AF_INET6)
		result = (ares_inet_pton(AF_INET6, name, &in6) < 1 ? 0 : 1);

	if (!result)
		return 0;

	if (family == AF_INET)
	{
		hostent.h_length = (int)sizeof(struct in_addr);
		addrs[0] = (char *)&in;
	}
	else if (family == AF_INET6)
	{
		hostent.h_length = (int)sizeof(struct ares_in6_addr);
		addrs[0] = (char *)&in6;
	}
	/* Duplicate the name, to avoid a constness violation. */
	hostent.h_name = ares_strdup(name);
	if (!hostent.h_name)
	{
		callback(arg, ARES_ENOMEM, 0, NULL);
		return 1;
	}

	/* Fill in the rest of the host structure and terminate the query. */
	addrs[1] = NULL;
	hostent.h_aliases = aliases;
	hostent.h_addrtype = aresx_sitoss(family);
	hostent.h_addr_list = addrs;
	callback(arg, ARES_SUCCESS, 0, &hostent);

	ares_free((char *)(hostent.h_name));
	return 1;
}

/* This is an API method */
int ares_gethostbyname_file(ares_channel channel, const char *name,
	int family, struct hostent **host)
{
	int result;

	/* We only take the channel to ensure that ares_init() been called. */
	if (channel == NULL)
	{
		/* Anything will do, really.  This seems fine, and is consistent with
		   other error cases. */
		*host = NULL;
		return ARES_ENOTFOUND;
	}

	/* Just chain to the internal implementation we use here; it's exactly
	 * what we want.
	 */
	result = file_lookup(name, family, host);
	if (result != ARES_SUCCESS)
	{
		/* We guarantee a NULL hostent on failure. */
		*host = NULL;
	}
	return result;
}

static int file_lookup(const char *name, int family, struct hostent **host)
{
	FILE *fp;
	char **alias;
	int status;
	int error;

#ifdef WIN32
	TCHAR PATH_HOSTS[MAX_PATH];
	win_platform platform;

	PATH_HOSTS[0] = '\0';

	platform = ares__getplatform();

	if (platform == WIN_NT) {
		TCHAR tmp[MAX_PATH];
		HKEY hkeyHosts;

		if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, WIN_NS_NT_KEY, 0, KEY_READ,
			&hkeyHosts) == ERROR_SUCCESS)
		{
			DWORD dwLength = MAX_PATH;
			RegQueryValueEx(hkeyHosts, DATABASEPATH, NULL, NULL, (LPBYTE)tmp,
				&dwLength);
			ExpandEnvironmentStrings(tmp, PATH_HOSTS, MAX_PATH);
			RegCloseKey(hkeyHosts);
		}
	}
	else if (platform == WIN_9X)
		GetWindowsDirectory(PATH_HOSTS, MAX_PATH);
	else
		return ARES_ENOTFOUND;

	wcscat_s(PATH_HOSTS, sizeof(WIN_PATH_HOSTS), WIN_PATH_HOSTS);

#elif defined(WATT32)
	extern const char *_w32_GetHostsFile(void);
	const char *PATH_HOSTS = _w32_GetHostsFile();

	if (!PATH_HOSTS)
		return ARES_ENOTFOUND;
#endif

	_wfopen_s(&fp, PATH_HOSTS, L"r");
	if (!fp)
	{
		error = ERRNO;
		switch (error)
		{
		case ENOENT:
		case ESRCH:
			return ARES_ENOTFOUND;
		default:
			DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
				error, strerror(error)));
			DEBUGF(fprintf(stderr, "Error opening file: %ls\n",
				PATH_HOSTS));
			*host = NULL;
			return ARES_EFILE;
		}
	}
	while ((status = ares__get_hostent(fp, family, host)) == ARES_SUCCESS)
	{
		if (strcasecmp((*host)->h_name, name) == 0)
			break;
		for (alias = (*host)->h_aliases; *alias; alias++)
		{
			if (strcasecmp(*alias, name) == 0)
				break;
		}
		if (*alias)
			break;
		ares_free_hostent(*host);
	}
	fclose(fp);
	if (status == ARES_EOF)
		status = ARES_ENOTFOUND;
	if (status != ARES_SUCCESS)
		*host = NULL;
	return status;
}

static void sort_addresses(struct hostent *host,
	const struct apattern *sortlist, int nsort)
{
	struct in_addr a1, a2;
	int i1, i2, ind1, ind2;

	/* This is a simple insertion sort, not optimized at all.  i1 walks
	 * through the address list, with the loop invariant that everything
	 * to the left of i1 is sorted.  In the loop body, the value at i1 is moved
	 * back through the list (via i2) until it is in sorted order.
	 */
	for (i1 = 0; host->h_addr_list[i1]; i1++)
	{
		memcpy(&a1, host->h_addr_list[i1], sizeof(struct in_addr));
		ind1 = get_address_index(&a1, sortlist, nsort);
		for (i2 = i1 - 1; i2 >= 0; i2--)
		{
			memcpy(&a2, host->h_addr_list[i2], sizeof(struct in_addr));
			ind2 = get_address_index(&a2, sortlist, nsort);
			if (ind2 <= ind1)
				break;
			memcpy(host->h_addr_list[i2 + 1], &a2, sizeof(struct in_addr));
		}
		memcpy(host->h_addr_list[i2 + 1], &a1, sizeof(struct in_addr));
	}
}

/* Find the first entry in sortlist which matches addr.  Return nsort
 * if none of them match.
 */
static int get_address_index(const struct in_addr *addr,
	const struct apattern *sortlist,
	int nsort)
{
	int i;

	for (i = 0; i < nsort; i++)
	{
		if (sortlist[i].family != AF_INET)
			continue;
		if (sortlist[i].type == PATTERN_MASK)
		{
			if ((addr->s_addr & sortlist[i].mask.addr4.s_addr)
				== sortlist[i].addrV4.s_addr)
				break;
		}
		else
		{
			if (!ares__bitncmp(&addr->s_addr, &sortlist[i].addrV4.s_addr,
				sortlist[i].mask.bits))
				break;
		}
	}
	return i;
}

static void sort6_addresses(struct hostent *host,
	const struct apattern *sortlist, int nsort)
{
	struct ares_in6_addr a1, a2;
	int i1, i2, ind1, ind2;

	/* This is a simple insertion sort, not optimized at all.  i1 walks
	 * through the address list, with the loop invariant that everything
	 * to the left of i1 is sorted.  In the loop body, the value at i1 is moved
	 * back through the list (via i2) until it is in sorted order.
	 */
	for (i1 = 0; host->h_addr_list[i1]; i1++)
	{
		memcpy(&a1, host->h_addr_list[i1], sizeof(struct ares_in6_addr));
		ind1 = get6_address_index(&a1, sortlist, nsort);
		for (i2 = i1 - 1; i2 >= 0; i2--)
		{
			memcpy(&a2, host->h_addr_list[i2], sizeof(struct ares_in6_addr));
			ind2 = get6_address_index(&a2, sortlist, nsort);
			if (ind2 <= ind1)
				break;
			memcpy(host->h_addr_list[i2 + 1], &a2, sizeof(struct ares_in6_addr));
		}
		memcpy(host->h_addr_list[i2 + 1], &a1, sizeof(struct ares_in6_addr));
	}
}

/* Find the first entry in sortlist which matches addr.  Return nsort
 * if none of them match.
 */
static int get6_address_index(const struct ares_in6_addr *addr,
	const struct apattern *sortlist,
	int nsort)
{
	int i;

	for (i = 0; i < nsort; i++)
	{
		if (sortlist[i].family != AF_INET6)
			continue;
		if (!ares__bitncmp(addr, &sortlist[i].addrV6, sortlist[i].mask.bits))
			break;
	}
	return i;
}